(1) Field of the Invention
The invention relates to an electromagnetic interference (EMI) prevention structure, and more particularly, to an electromagnetic interference prevention structure for a personal computer.
(2) Description of the Prior Art
Many electronic products, especially information products such as personal computers or set-top boxes, comprise metal housings for covering a main board of a computer system, so as to protect the electronic components therein and to reduce EMI for the electronic components. It has been proven that strong EMI generated by an electronic product can cause harm to a human being, especially for electronic devices having high working frequencies. Therefore, a specified security standard to limit the level of EMI from many kinds of the electronic products is applied in many countries.
In a conventional technique, a main board in a metal housing is usually fixed into an inner side or the metal housing by screws so as to reduce the potential between the ground voltage of the main board and voltage of the metal housing. Thus, the EMI generated from the potential can be reduced. Additionally, the conductive surface can be extended because of the contact between the main board and the metal housing so that the energy of the EMI may be decreased.
FIG. 1 shows a main board of a computer system 10 according to the prior art, wherein an upper cover of the housing is removed such that the relationship between a main board 11 and a metal housing 13 is clear. A plurality of through holes 15 are formed on the main board 11 so that the main board 11 can be secured on one surface of the metal housing 13 by screws 12. The lower portion of the screw 12 is tinned and is connected with a ground layer 14 of the main board 11 so as to reduce a potential between a voltage of the main board 11 and a voltage of the metal housing 13. Thus, the EMI generated from the potential can be reduced. Additionally, the conductive surface can be extended because of the contact between the main board 11 and the metal housing 13 so that the energy of the EMI may also be reduced.
However, securing the screws 12 and the metal housing 13 is difficult. Moreover, the screws allow for a gap between the metal housing 13 and the main board 11, the gap permitting electromagnetic waves to easily pass through.
Accordingly, it is a primary object of the present invention to provide a computer system and an EMI preventing structure thereof.
To achieve the above object the present invention provides a shielding device comprising a pair of substantially parallel metal plates and a metal side plate forming an open rectangular channel, said shielding device connected to a ground layer of a main board by clamping over a periphery thereof, wherein at least one spring piece is installed on at least one of the metal plates for mating with a leading groove of a computer housing.
This object is achieved by the EMI preventing structure described below.